<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box1 {
      box-sizing: content-box;

      width: 100px;
      height: 100px;
      background-color: #f00;

      padding: 30px;
      border: 10px solid orange;
    }

    .box2 {
      box-sizing: border-box;
      width: 100px;
      height: 100px;
      background-color: #0f0;

      padding: 30px;
      border: 10px solid purple;
    }
  </style>
</head>

<body>


  <div class="box1"></div>
  <div class="box2"></div>

</body>

</html>